SPECTRUM MATCHING SCALING PROCEDURES APPLIED TO NONLINEAR ANALYSIS OF WHARVES

Wharf structures are essential structures in the economy of a country. Even though their importance, they have received less attention compared with ordinary buildings. These structures are characterized by significant torsional response under bi-directional earthquakes excitations. This behavior arises for the changes in lengths of piles from the land side or waterside. On the other side, they support a complex state of static and dynamic load due to water Streams, impact with containers and craine effects, etc. The ASCE/COPRI 61 – 14 [1] demand that analysis and design of wharves structures have to been done with nonlinear – time history analysis and this motivates this research to present a procedure for selecting and scaling of ground motions for nonlinear dynamic analysis. A recently developed scaling procedure called the modal pushover-based scaling (MPS) [2] has been successfully implemented in the seismic analysis of single and multi-story buildings with symmetric or unsymmetrical structural plan distribution. An extension of the well-known Spectrum Matching methodology is presented here to analyze wharf structures. Sophisticated non-linear dynamic analysis is conducted on four different types of wharves subjected to one suite of 7 ground motions each. The suite corresponds to near-field records that represent the seismicity of Los Angeles area. Pairs of wharves with length varying from 300 to 600m are analyzed; for each length, two embankment systems are defined as 2:1 and 3.5:1. The performance of these structures is compared with benchmark values defined as the mean values of Engineering Demand Parameters (EDPs) due to a more extensive suite of unscaled records. Additionally, this study is compared with the ASCE/SEI 7-10 [3] procedure for selecting and scaling records. Results indicate that SM scaling procedure can result in an improvement of results obtained with ASCE/SEI7-10, with lower underestimation of the platform drifts demand by as much as 10% and underestimation of the material strain demands by as much as 30%. Also, ASCE/SEI 7-10 methodology underestimates the displacements of wharves structures in values ranging from 30-40% and material strain demands of up to 60%, respectively. Moreover, it is found that the MPS procedure provides better estimates of the expected EDPs. Because the performance acceptance in the new standard ASCE/COPRI 61-14 [1] (seismic design of piers and wharves) is solely based on strain limits, the Spectrum Matching (SM) scaling procedure could lead to unconservative results.